Cathode assemblies and electrolytic cells containing same



1962 A. .1. WHITNEY 3,061,535

CATHODE ASSEMBLIES AND ELECTROLYTIC CELLS CONTAINING SAME Filed Aug. 31, 1959 2 Sheets-Sheet 1 FIG.||

ARTHUR J.WH|TNEY INVENTOR.

W f, M

A. J. WHITNEY Oct. 30, 1962 CATHODE ASSEMBLIES AND ELECTROLYTIC CELLS CONTAINING SAME 2 Sheets-Sheet 2 Filed Aug. 51, 1959 FIG.II|

ne w l/I i ARTHUR J. WHITNEY The present invention relates to novel cathode assemblies for electrolytic cells, and to such cells containing such assemblies for fused salt electrolysis and, for example, for electrolysis of a molten alkali metal salt to produce an alkali metal. More particularly, the invention relates to novel cathode assemblies and cells containing same adapted for electrolysis of a molten salt electrolyte, such as sodium chloride, to produce sodium metal.

Those skilled in the art are aware of numerous disclosures pertaining to electrolytic cells of various types adapted for fused salt electrolysis of molten salts and, for illustrative purposes, a cell for such a purpose is disclosed in US. Patent No. 2,592,483. By use of such a cell, the chemical compound or compounds to be electrolyzed are maintained as a liquid bath in the cell in which an anode and cathode, or a plurality thereof, are disposed in suitable manner whereby the desired decomposition is effected by electrolytic means. A specific illustration relates to decomposition of sodium chloride into sodium and chlorine by maintaining, in a vessel containing a suitable electrolytic cell, a molten bath containing sodium chloride at an elevated temperature (e.g., about 550 to 650 C.) with operation of the cell at a voltage of about 6 to about 7 volts, depending on amperage.

In cells normally used for such a purpose, the electrodes are separated by a narrow annular space as fused salts are relatively poor conductors, particularly when compared with aqueous solutions of electrolytes, so as to avoid undue power consumption per pound of metal obtained. Moreover, in the production of a metal by electrolysis of a fused salt, it is generally necessary to use a mixture of a salt of the desired metal with one or more salts of another metal or metals in order to provide for the electrolysis an electrolyte having a suitable melting point. Thus, in the production of sodium by electrolysis of sodium chloride, a suitable substance such as calcium chloride is used in mixture with sodium chloride, the amount of the calcium compound employed being controlled so as to provide a mixture of suitable melting point and in which mixture the concentration of calcium is such that formation of an undesired separate phase of calcium is avoided or minimized during operation of the cell. For example, in a typical operation of a sodium cell, a suitable mixture for the electrolysis operation may consist of about 42 weight percent sodium chloride and 58 Weight percent calcium chloride.

In existing cells, and particularly those commonly used for fused salt electrolysis of a molten alkali metalsalt, the cathode consists of a heavy walled tube or a multiplicity thereof, nested together by weldments and braces, suspended vertically in the cell by means of diametrically opposed cast steel arms that protrude through the sidewalls of the cell. Generally, the steel arms are welded to the tube walls whereby the tubes form primary structural members in addition to serving as current carriers for the electrolysis. Typical structures thereof are disclosed in the art as, for example, in US. Patents Nos. 2,592,483; 2,865,833; and others. 7

Although such cathodic structures have been and are still being used for electrolysis of fused salts, they are subject to certain disadvantages. For example, in addition to entailing high initial construction costs, they are rates at 1 Patented Oct. 30, 1962 "ice ' subject to objectionable distortion during operation of the cell containing such cathode structures, thereby necessitating re-boring or scrapping of the cathode. Such distortion is generally caused by the fact that the cathode tubes are of substantially heavy gauge metal and the tubes are primary structural members that carry all of the weight and absorb strains that affect the cathode. Accordingly, and as compared to such cathodic structures, it is highly desirable to make available a cathode assembly that (1) requires lower initial construction costs and is capable of being mass produced without requiring extensive, if any, boring, (2) can be made from lighter gauge metal whereby the cathode assembly can be handled more easily and, in particular, facilitate positioning during installation, (3) is subject to much less, if any, distortion during operation of the cell containing the cathodic structure thereby decreasing maintenance costs due to elimination or minimization of re-boring requirements and lengthening the life of the cathode, (4) is capable of being more easily replaced, when necessary, and (5) possesses flexibility of design such that it can be easily modified to accommodate multiple cathode tube arrangements as the need for such arrangements arise.

The main object of this invention is to provide a novel, improved cathode assembly, and electrolytic cells containing same, for electrolysis of fused salts with obtainment of the numerous aforesaid advantages set forth hereinbefore.

In accordance with this invention, there is provided a cathode assembly that comprises an elongated main support member having at each end portion thereof means adapted to connect a source of electrical current to said support member, at least two vertically elongated cathode support members on one side of said main support member and in electrical current-carrying relationship, said cathode support members being spaced apart from each other and intermediate the said end portion of the main support member, a vertically elongated hollow cathode disposed in between said cathode support members and supported by said members in electrical current-carrying relationship, at least two other vertically elongated cathode support members disposed on the other side of said main support member, said other cathode support members being spaced apart from each other and intermediate the end portion of the main support means, and a vertically elongated hollow cathode disposed in between said other cathode support members and supported thereby in electrical current-carrying relationship.

In a specific embodiment, the novel cathode assemblies embodied herein comprise an elongated metal main support plate having means at each end portion adapted to connect said plate to a source of electrical current, such as a bus bar, at least two vertically elongated wing plates disposed substantially perpendicular to said main support plate, one edge of each of said wing plates being adhered in electrical current-carrying relationship to said main support plate, said wing plates being spaced apart from and substantially parallel to each other, a vertically elongated hollow cathode disposed in between said wing plates, said cathode being welded to each of said wing plates, at least two other wing plates perpendicularly disposed on the opposite side of said main support plate, said other wing plates being vertically elongated, spaced apart from and substantially parallel to each other and intermediate the end portions of said main support plate with on edge of each of said other wing plates being adhered in electrical current-carrying relationship with said main support plate, and a vertically elongated hollow cathode disposed in between said other wing plates and welded to each of said other wing plates.

In order to further describe the invention, reference is made to the accompanying drawings wherein there is shown an embodiment of a novel cathode assembly as embodied herein, and its disposition in an electrolytic cell adapted for electrolysis of a fused alkali metal salt (e.g., sodium chloride).

In FIGURE I, there is shown a plan view of a cathode assembly as embodied herein; in FIGURE II there is shown partly in elevation the embodiments of FIGURE I; and in FIGURE III there is shown partly in elevation and partly in cross section a cathode assembly of the embodiment of FIGURE I disposed in an electrolytic cell, suitable for electrolysis of a fused alkali metal salt, of the type illustrated in U.S. Patent No. 2,592,483.

In FIGURES I and II, a cathode assembly is shown that comprises a main elongated support plate 52 having end portions provided with suitable openings 56a for engagement with means, such as a bus bar, for a source of supply of electrical current to the support plate 52. As shown, there is attached to main support plate 52 a wing plate 53, a wing plate 54 and, on the opposite side of support plate 52, a set of wing plates corresponding to the disposition of wing plates 53 and 54. Such other wing plates comprise wing plate 55 and wing plate 56. As shown, each wing plate is adhered to the main support plate 52 by Welding one edge of the wing plate to the main support plate. Thus, wing plate 53 is welded to plate 52 by means of welds 57; wing plate 54- welded to plate 52 by Welds S8; wing plate 55 is welded to plate 52 by Welds 59; and wing plate 56 is welded to plate 52 by welds 60. As is further shown, the Wing plates are spaced apart from each other, are substantially parallel, are supported by the main plate 52 intermediate the end portions of plate 52 and are substantially perpendicular to plate 52. Further, in the embodiment shown, the wing plates are substantially equal in length (i.e., from the plate 52) to the radius of the cathode tubes and the wing plates are spaced apart for a distance substantially equal to the diameter of the cathode tubes whereby the tubes, disposed in between the wing plates, are easily welded to the end of the wing plates. Since, in considering that electrical current travels from positive to negative, the current flow travels from the anode (in the electrolytic cell) across the space to the cathode and then through the wing plates. Hence, in the described embodiment, the cathode tubes are welded to the Wing plates with a longitudinal Weld sufficient to provide adequate current-carrying capacity for operation of the cell in which the cathode assembly is used.

Although FIGURES I and II show an embodiment of the cathode assembly with at least four nested cathode tubes, it should be understood that it is an embodiment to which the invention is not limited. Thus, the invention embodies such an assembly using only two cathode tubes and, which, using FIGURES I and II for illustration, comprises plate 52, wing plates 53 and 54 on one side of the plate 52 and wing plates 55 and 56 on the other side with cathode tube 50 in between plates 53 and 54 and cathode tube 50" in between plates 55 and 56 with elimination of cathode tubes 50 and 50" and wing plates on the righthand side of said latter two cathode tubes. On the other hand, and again using FIGURES I and II for illustration, cathode assemblies embodied herein may comprise more cathode tubes than are shown in said FIG- URES I and II in which case main support plate 52 is of sufficient length to accommodate additional wing plates and appropriate cathode tubes in between said additional wing plates, each of said cathode tubes being supported in the same manner as described with reference to FIGURES I and II.

Reference is now made to FIGURE III showing an electrolytic cell, of the type illustrated in U.S. Patent No. 2,592,483, with a cathode assembly as shown in FIG- URES I and II. FIGURE III shows the lower portion of a fused salt electrolysis cell of cylindrical shape in which graphite anodes 1 and 1 are disposed, each of said anodes being surrounded coaxially by steel hollow cathodes 50 and 50', respectively. Each anode is supported by base plate 4 which is a circular steel plate horizontally disposed and has formed therein anode socket 5. The base plate 4 and anode socket 5 may be a single, integral casting or the socket and base plate may be separately formed and welded together. At its periphery, plate 4- is provided with an upstanding flange 10. Base plate 4 is supported by beams 25 and insulators 26 which insulate the base plate and anodes from ground.

The anodes 1 and 1 are surrounded, as shown, by a layer of annular refractory cement 12. The side walls of the cell are formed by cylindrical steel shell 11 which is open at both ends and is provided with two suitable openings to receive cathode arms 51 and 51'. The diameter of shell 11 is less than the diameter of plate 4 so that when shell 11 is centered there is an annular space between the shell 11 and flange 10. In constructing the cell, three or four insulating refractory bricks 33 are placed on plate 4 to support the shell. Refractory insulating cement 12 is then placed in the annular space between shell 11 and the anodes and in the annular space between shell 11 and flange 10. The layer of refractory cement 12 is sufficiently thick to cover the top of anode socket 5. After the refractory cement has set, shell 11 is lined with refractory brick 13 or other suitable refractory in conventional manner and, during this operation the cathode assembly is installed. In order to install the cathode With the arms 51 and 51' projecting through the sides of the cell, shell 11 is formed in two halves which are fastened together by conventional means, e.g., flanges 18 and bolts 19 after the cathode has been set in place thereby forming an upper half and a lower half of the cell. Cathode arms 51 and 51 are sealed by refractory cement 20 held in place by flanges 21 or other suitable means. The cell is completed by adding other conventional elements such as shown in the drawing (FIGURE III) and including a collector ring and dome support assembly 14, diaphragms 7 and 7 supported by the collector ring assembly, and riser pipe 16 which serves to lead molten alkali metal to a cell receiver (not shown). Anode bus bar 22 is fastened to the base of anode socket 5 by means of bolts 23. For cooling the bottom portion of the anodes and cell, suitable means such as water jacket 40 is provided as shown, with conduit means 41 being adapted for introducing cooling means, such as water, into jacket 40 and conduit means 42 for withdrawal of cooling Water from jacket 40. For cooling the cathode arm contacts, such cooling can be effected by introducing cooling water into a hollow surface section (not shown) in the cathode arms 51 and 51' through use of conduit means for introduction of cooling water and Withdrawal of effluent from the hollow section.

As is further shown in FIGURE III, wherein a multianode cell is described, anode 1 is surrounded by :1 dia phragm 7 and anode 1 by diaphragm 7 and each anode and its adjacent diaphragm is surrounded by a cathode, i.e., anode 1|by cathode 50 and anode 1 by cathode 50. Though not shown, and with use of the assembly of FIG- URE I in the cell of FIGURE III, a corresponding set of cathodes 50 and 50 is disposed on the opposite side of center beam support 52. In such an embodiment, cathode 50 is welded to the ends of wing plates 53 and 54; cathode 50' to the ends of wing plates 54 and another wing plate (not shown) to the right of cathode 50; cathode 50 to the ends of wing plates 55 and 56; and cathode 50' to the ends of wing plates 56 and another wing plate (not shown) to the right of cathode 50".

Although cathodes of hollow cylindrical shape have been used in the foregoing description of the invention in connection with the described embodiments for illustrative purposes, the invention can be carried out with cathodes that are hollow but of shape other than cylindrical. Thus, cathodes that have a square, elliptical, triangular,

or other shape may be used and adhered, as by welding, to the wing plates in assemblies as .aforedescribed.

By practice of this invention, it has been found that cathodes from metal as thin as A in. wall thickness (mild steel, cast steel, etc.) can be used without undergoing objectionable, if any, distortion over the period of normal cell life whereas cathodes of metal as thick as to 1", when supported by the cathode arms in conventional manner and serve as primary structural members, generally undergo distortion over a corresponding period of cell operation. Such improved results with cathode assemblies as embodied herein, while otherwise operating at least equally as satisfactory as conventional cathode assemblies in other respects in conventional electrolysis of a sodium chloride-containing fused bath, have been obtained, for example by use of the novel cathode assemblies wherein the main support plate (i.e., plate 52 in FIGURE 1) is mild steel of the following dimensions: 1" thick x 36" wide X 95" long; and the wing plates are mild steel /2 to thick, wide and 36 long; and the cathode tubes are welded to the wing plates with /2" fillets, 36 long, the cathode tubes having dimensions of A thick, 40" long and 18 /2 in diameter.

Although the invention, in specific embodiments, has been described in connection with the drawings wherein the novel cathode assembly has been fabricated by use of wing plates welded to a main support plate (52) and to which separate arms (51 and 51') adapted for engagement with a bus bar are attached, it is within the scope of this invention that the assembly be fabricated in other ways as, for example, by casting the complete assembly or multiple portions thereof followed by assembly of said portions as, for example, by welding.

In reference to the cathodes which, as aforesaid, may be in the form of any of several different shapes, there may be used cathodes of slotted design as, for example, as described in co-pending application Serial No. 668,- 417, filed June 27, 1957, now Patent 2,913,387. Use of such slotted cathodes, in combination with a deflector shield disposed as described in said co-pending applica tion, provide material advantages in cell operation mainly in that they permit transfer, passage and removal from the cell of molten cathodic products substantially out of contact with reactive gaseous anodic products. Thus, when slotted cathodes are used, a deflector means is also preferably used and, for example, is supported by stiifener bars '63 and 64 (FIGURES I and II) on cathodes 63 and 64, respectively. Thus, though not shown herein, the present invention embodies use in the novel assemblies of such slotted cathodes with obtainment of the stated material advantages over and above those advantages provided by the novel structure embodied herein for support of the cathodes.

While there are above disclosed but a limited number of embodiments of the invention herein presented, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is desired therefore that only such limitations be imposed on the appended claims as are stated therein.

What is claimed is:

1. A cathode assembly comprising an elongated vertically disposed main support member in the form of a plate having at each end portion thereof means adapted to connect a source of electrical current to said main support member, at least two vertically elongated wing plates extending outwardly from said main support member on one side thereof and in substantially perpendicular relationship with respect thereto, said wing plates being spaced apart in substantially parallel relationship and providing a pair of cathode support plates in electrical current-carrying relationship with respect to said main support member, a vertically elongated tubular cathode secured between said pair of cathode support plates in electrical current-carrying relationship with respect thereto, at least two additional wing plates extending outwardly from said main support member on the opposite side thereof in substantially perpendicular relationship with respect thereto, said additional Wing plates being spaced apart in substantially parallel relationship and providing a second pair of cathode support plates in electrical current-carrying relationship with respect to said main support member, and a vertically elongated tubular cathode secured between said second pair of cathode support plates in electrical current-carrying relationship with respect thereto.

2. A fused salt electrolysis cell having refractory-lined side walls and a metal bottom, an elongated vertically disposed main support member in the form of a plate extending through diametrically opposite Wall portions of said cell, each projecting extremity of said main support member having means adapted to connect a source of electrical current thereto, at least two vertically elongated wing plates extending outwardly from said main support member on one side thereof and in substantially perpendicular relationship with respect thereto, said wing plates being spaced apart in substantially parallel relationship and providing a pair of cathode support plates in electrical current-carrying relationship with respect to said main support member, a vertically elongated tubular cathode secured between said pair of cathode support plates in electrical current-carrying relationship with respect thereto, an anode extending upwardly from the bottom of and into the electrolysis zone of said cell, said anode being spaced from and surrounded by said tubular cathode, at least two additional Wing plates extending outwardly from said main support member on the opposite side thereof in substantially perpendicular relationship with respect thereto, said additional wing plates being spaced apart in substantial parallel relationship and providing a second pair of cathode support plates in electrical current-carrying relationship with respect to said main support member, a vertically elongated tubular cathode secured between said second pair of cathode support plates in electrical current-carrying relationship with respect thereto, and an anode extending upwardly from the bottom of and into the electrolysis zone of said cell, said anode being spaced from and surrounded by said last mentioned tubular cathode.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A CATHODE ASSEMBLY COMPRISING AN ELONGATED VERTICALLY DISPOSED MAIN SUPPOET MEMBER IN THE FORM OF A PLATE HAVING AT EACH END PORTION THEREOF MEANS ADAPTED TO CONNECT A SOURCE OF ELECTRICAL CURRENT TO SAID MAIN SUPPORT MEMBER, AT LEAST TWO VERTICALLY ELONGATED WING PLATES EXTENDING OUTWARDLY FROM SAID MAIN SUPPORT MEMBER ON ONE SIDE THEREOF AND IN SUBSTANTIALLY PERPENDICULAR RELATIONSHIP WITH RESPECT THERETO, SAID WING PLATES BEING SPACED APART IN SUBSTANTIALLY PARALLEL RELATIONSHIP AND PROVIDING A PAIR OF CATHODE SUPPORT PLATES IN ELECTRICAL CURRENT-CARRYING RELATIONSHIP WITH RESPECT TO SAID MAIN SUPPORT MEMBER, A VERTICALLY ELONGATED TUBULAR CATHODE SECURED BETWEEN SAID PAIR OF CATHODE SUPPORT PLATES IN ELECTRICAL CURRENT-CARRYING RELATIONSHIP WITH REPECT THERETO, AT LEAST TWO ADDITIONAL WING PLATES EXTENDING OUTWARDLY FROM SAID MAIN SUPPORT MEMBER ON THE OPPOSITE SIDE THEREOF IN SUBSTANTIALLY PERPENDICULAR RELATIONSHIP WITH RESPECT THERETO, SAID ADDDITIONAL WING PLATES BEING SPACED APART IN SUBSTANTIALLY PARALLED RELATIONSHIP AND PROVIDING A SECOND PAIR OF CATHODE SUPPORT PLATED IN ELECTRICAL CURRENT-CARRYING RELATIONSHIP WITH RESPECT TO SAID MAIN SUPPORT MEMBER, AND A VERTICALLY ELONGATED TUBULAR CATHODE SECURED BETWEEN SAID SECOND PAIR OF CATHODE SUPPORT PLATES IN ELECTRICAL CURRENT-CARRYING RELATIONSHIP WITH RESPECT THERETO. 